Elon was irritated that he was behind in the AI intellectual property race and this narrative created a perfect opportunity. Not surprised in the end. Tesla effectively did the same thing - "come help me save the planet" with overpriced cars. [Edit: Apparently Elon has left OpenAI but I don't believe for a second that he will not participate in this LP]
The OpenAI staff are literally some of the most employable folks on earth; if they have a problem with the new mission it's incredibly easy for them to leave and find something else.
Additionally, I think there's a reason to give Sam the benefit of the doubt. YC has made multiple risky bets that were in line with their stated mission rather than a clear profit motive. For example, adding nonprofits to the batch and supporting UBI research.
Their's nothing wrong with having a profit motive or using the upsides of capitalism to further their goals.